As is well known, vehicles, and in particular large trucks, are provided with scissors-type suspensions capable of cushioning extremely heavy loads unlike those normally encountered in the smoother ride of a passenger car. In order to isolate the driver from fatigue and discomfort induced by the vehicle vibrations, it is normal practice to provide seat suspension systems incorporating various spring arrangements which protect the driver from vibrations at the expense of consuming a considerable amount of physical space beneath the seat. This is especially applicable to spring suspension systems which can be adjusted according to the weight of the seat occupant. Some of these seats include slide provisions which enable a fore and aft or longitudinal adjustment of the seat relative to the floor of the vehicle. When a seat is provided with both of the aforementioned adjustments, it must locate its seat frame a considerable distance above the vehicle floor to accommodate them. In addition, the partial collapsibility of the scissors linkage used in the suspensions also contributes to the distance at which the seat is mounted. Often, this distance becomes prohibitively high to be utilized in certain vehicles having relatively small space limitations between the floor and the ceiling. Accordingly, it remains desirable to provide a seat suspension incorporating both a seat occupant weight compensation adjustment and a fore and aft seat adjustment which together with a substantially fully collapsible scissors linkage will ensure a relatively low profile for the seat.
One such seat suspension is disclosed in U.S. Pat. No. 5,765,802 issued Jun. 16, 1998 and U.S. Pat. No. 5,871,198 issued Feb. 16, 1999, both of which are assigned to the assignee of this application. In these patents, a seat suspension includes a fore and aft seat adjustment mechanism and a weight compensation adjustment mechanism in combination with a substantially fully collapsible scissors linkage. While the designs from these patents have performed satisfactorily, improvements can be made to further enhance the performance, ease of adjustment and economy of cost for the seat suspension. For example, in the aforementioned patents, the weight compensation adjustment mechanism is located on the left side of the seat such that upon a forward seat adjustment it is sometimes difficult to access the adjustment knob which may have moved rearwardly beyond the reach of the seat occupant. Moving the adjustment knob to the front of the seat however requires that the weight compensation adjustment mechanism allow the adjustment knob to move back and forth with the fore and aft seat adjustment.
It is a principal object of the present invention to provide a suspension mechanism that is simply constructed and relatively inexpensive while still meeting manufacturers' ever increasing demands for compactness and comfort.
It is also an object of the present invention to provide a suitable suspension unit which will reduce the shocks and vibration transmitted from the vehicle to the driver via the driver's seat.
It is a further object of the present invention to provide a seat suspension having an adjustable preload to suit the weight of the seat occupant.
It is another object of the present invention to provide a seat suspension utilizing a scissors linkage having slide channels which serve as guides for the longitudinal adjustment of the seat.
Yet another object of the present invention to provide a seat suspension having a substantially fully collapsible scissors linkage.
It is also an object of the present invention to provide a seat suspension with a weight compensation adjustment which is always accessible irregardless of the longitudinal adjustment of the seat.
In one aspect of the invention, a low profile seat suspension includes a bottom frame adapted to be mounted on a vehicle, and a top frame located above the bottom frame for supporting a seat cushion and seat back thereon. A substantially fully collapsible scissors linkage is interconnected between the bottom frame and the top frame enabling the bottom frame and the top frame to move relative to each other substantially in parallelism. A biasing arrangement is disposed between the top frame and the bottom frame and has a preload force urging the top frame away from the bottom frame. A first adjustment mechanism is located in the top frame and selectively enables fore and aft adjustment of the top frame relative to the bottom frame. A second adjustment mechanism is located between the bottom frame and the top frame and selectively enables an adjustment on the biasing arrangement in accordance with the weight of an occupant in the seat by translating a horizontal force applied to an adjustment plate into a vertical force affecting the preload force of the biasing arrangement. The adjustment plate has a cam engaged therewith and the horizontal force slidably moves the adjustment plate and cams a resilient element of the biasing arrangement in a vertical direction. The invention is improved wherein an adjustment knob of the second adjustment mechanism is positioned at a front of the seat and the knob is enabled to move along with the top frame irregardless of the fore and aft adjustment of the top frame relative to the bottom frame.
Various other objects, features and advantages of the invention will be made apparent from the following description taken together with the drawings.